Various types of combustors are known and are in use in gas turbine engines. In turn, these combustors use different types of fuel nozzles depending upon the type of fuel in use. For example, most natural gas fired systems operate using lean premixed flames. In these systems, fuel is mixed with air upstream of the reaction zone for creating a premix flame. One example is a “swozzle” (swirler+nozzle) in which the fuel ports are positioned about a number of vanes. Alternatively in most syngas based systems, diffusion nozzles may be used that inject the fuel and air directly into the combustion chamber due to the higher reactivity of the fuel.
Due to the significant differences between the characteristics of natural gas and syngas in Wobbe number and fuel reactivity, traditional vane hole injector designs used for natural gas systems may create flame holding problems if used for syngas. Likewise, a diffusion nozzle may result in high NOX emissions unless a diluent is injected.
Alternative technology for syngas combustion is being developed that allows for some syngas premixing while reducing the potential for flame holding by using co-flow injection of the fuel into the air. Such an injection method, however, may not allow for stabilizing a natural gas flame.
There is thus a desire for a turbine combustion system that can operate with a variety of fuels with differing characteristics. The system should be fuel flexible while maintaining reduced emissions and high efficiency over a variety of operating conditions.